1. Field of the Invention
The present invention relates to a method of filling a liquid crystal display panel with liquid crystal and a liquid crystal filling system for performing the same.
2. Description of the Related Art
Generally, liquid crystal is interposed between a TFT substrate and a color filter substrate of a liquid crystal display panel.
The liquid crystal is affected by an electric field formed between the TFT substrate and the color filter substrate. In detail, the liquid crystal varies the transmissivity of the light supplied from an external light source depending on the electric field applied thereto, so that full-color images required by users can be displayed.
The TFT substrate and the color filter substrate have a cell gap for receiving the liquid crystal.
Since the cell gap has a size of a few micrometers (μm), a special method is required to uniformly supply liquid crystal over the entire area of the cell gap.
In order to fill the liquid crystal into the cell gap, firstly, a part of a liquid crystal display panel having the cell gap is firstly immersed into the liquid crystal contained in a barrel. Then, since vacuum pressure is formed in the cell gap, the liquid crystal is sucked into the cell gap.
The above method of filling liquid crystal using vacuum pressure has an advantage that the liquid crystal can be completely filled in the cell gap having the size of a few micrometers (μm), such that no empty area remains in the cell gap. However, an excessive amount of liquid crystal may be supplied into the cell gap.
For this reason, the above method of filling liquid crystal using vacuum pressure requires additional processes such as a pressing process for discharging excessively injected amount of liquid crystal, a liquid crystal sealing process for sealing an inlet and an outlet, through which the liquid crystal is respectively injected and discharged, with sealing materials, and a cleaning process for cleaning the liquid crystal remaining on an outer surface of the liquid crystal display panel.
Besides the liquid crystal filling method using vacuum-pressure, a second liquid crystal filling method has been recently developed.
According to the second liquid crystal filling method, first, the liquid crystal is dropped onto the color filter substrate. Then, the TFT substrate is bonded to the color filter substrate such that the liquid crystal is filled between the TFT substrate and the color filter substrate.
The second liquid crystal filling method may fill the liquid crystal between the TFT substrate and the color filter substrate in a relatively simple manner compared with the liquid crystal filling method using vacuum-pressure. However, according to the second liquid crystal filling method, bubbles are generated inside the liquid crystal display panel or the liquid crystal overflows the liquid crystal display panel.
For example, when an excessive amount of liquid crystal is supplied into the color filter substrate, the excessive amount of liquid crystal overflows outside of the liquid crystal display panel. On the contrary, when the liquid crystal is insufficiently supplied into the color filter substrate, a bubble area is formed inside the liquid crystal display panel. Since liquid crystal does not exist in the bubble area, image may not be displayed in the bubble area.
Accordingly, in the second liquid crystal filling method, it is important to determine a precise amount of liquid crystal to be supplied into the liquid crystal display panel.
The amount of liquid crystal supplied into the liquid crystal display panel is determined depending on a volume of spacers and an internal volume defined by a region enclosed by a seal line formed on the color filter substrate.
However, the internal volume and the volume of the spacers used for determining the amount of liquid crystal to be supplied may be varied depending on the liquid crystal filling process.
Especially, the volume of the spacers remarkably varies depending on substrates because of differences in the prosess of forming spacers.
The spacers are randomly attached to the region enclosed by the seal line of the color filter substrate by means of a spacer disperser. Since a random number of spacers are attached to the region enclosed by the seal line, measuring the total volume of the spacers is difficult.
For this reason, it is difficult to precisely calculate the total volume of the spacers. Therefore, the amount of liquid crystal to be supplied may not be precisely calculated.
On the other hand, the spacers may be formed through a process of patterning a photoresist film. In this case, a predetermined number of spacers are attached to predetermined positions on the substrate, so that the total volume of the spacers can be roughly calculated.
However, since a height of the photoresist film has a deviation depending on the positions on the substrate, the volume of the spacers may slightly vary depending on the positions of the spacer on the substrate. Therefore, it is difficult to precisely calculate the total volume of the spacers and the amount of liquid crystal to be supplied.